Arrangement for and method of projecting an image with linear scan lines

ABSTRACT

A lightweight, compact image projection module, especially for mounting in a housing having a light-transmissive window, is operative for sweeping a composite laser beam as a pattern of linear scan lines on a planar projection surface and for causing selected pixels arranged along each linear scan line to be illuminated to produce an image of high quality and in color.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/380,806, filed May 15, 2002, and is a continuation-in-partof U.S. patent application Ser. No. 10/427,528, filed May 1, 2003 nowU.S. Pat. No. 7,446,822.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to projecting a two-dimensionalimage of high quality especially in color.

2. Description of the Related Art

It is generally known to project a two-dimensional image on a projectionsurface based on a pair of scan mirrors which oscillate in mutuallyorthogonal directions to scan a laser beam over a raster patterncomprised of a plurality of scan lines. However, the known imageprojection systems project the image with curved scan lines, therebyimparting to the image a distortion which is difficult to correctelectronically.

SUMMARY OF THE INVENTION Objects of the Invention

Accordingly, it is a general object of this invention to provide animage projection arrangement that projects a two-dimensional image,especially in color, of high quality in accordance with the method ofthis invention.

Another object of this invention is to project the image with linearscan lines in such projection arrangements.

Yet another object of this invention is to reduce, if not eliminate,objectionable distorted images in such projection arrangements.

An additional object is to provide a miniature, compact, lightweight,and portable color image projection module useful in many instruments ofdifferent form factors.

Features of the Invention

In keeping with these objects and others, which will become apparenthereinafter, one feature of this invention resides, briefly stated, inan image projection arrangement for, and a method of, projecting atwo-dimensional image of high quality, especially in color. Thearrangement includes a laser assembly for directing a laser beam; ascanner including a scan mirror oscillatable about a scan axis, forsweeping the laser beam as a pattern of scan lines during oscillation ofthe scan mirror on a planar projection surface at a distance from thelaser assembly, each scan line having a number of pixels; and acontroller operatively connected to the laser assembly and the scanner,for causing selected pixels to be illuminated, and rendered visible, bythe laser beam to produce the image.

In accordance with one aspect of this invention, the laser beam isdirected to the scan mirror along an optical path in a plane, which isperpendicular to the scan axis. This enables each of the scan lines onthe planar projection surface to be linear, thereby reducing, if noteliminating, the image distortion caused by curved scan lines accordingto the prior art.

In the preferred embodiment, the laser assembly includes a plurality oflasers for respectively generating a plurality of laser beams ofdifferent wavelengths, for example, red, blue and green laser beams, andan optical assembly for focusing and nearly collinearly arranging thelaser beams to form the laser beam as a composite beam which is directedto the scan mirror. The scan mirror is operative for sweeping thecomposite beam along a first linear direction at a first scan rate andover a first scan angle. Another oscillatable scan mirror is operativefor sweeping the composite beam along a second direction substantiallyperpendicular to the first linear direction, and at a second scan ratedifferent from the first scan rate, and at a second scan angle differentfrom the first scan angle. At least one of the scan mirrors isoscillated by an inertial drive.

It is advantageous if a support is provided for supporting the laserassembly and the scanner. Preferably, the optical assembly includes afold mirror mounted on the support at an angle of inclination fordirecting the composite laser beam along the plane perpendicular to thescan axis.

The controller includes means for energizing the laser assembly toilluminate the selected pixels, and for deenergizing the laser assemblyto non-illuminate pixels other than the selected pixels. The controlleralso includes means for effectively aligning the laser beams collinearlyby delaying turning on and off the pixels of each of the laser beamsrelative to each other.

The support, lasers, scanner, controller and optical assembly preferablyoccupy a volume of less than thirty cubic centimeters, therebyconstituting a compact module, which is interchangeably mountable inhousings of different form factors, including, but not limited to, apen-shaped, gun-shaped or flashlight-shaped instrument, a personaldigital assistant, a pendant, a watch, a computer, and, in short, anyshape due to its compact and miniature size. The projected image can beused for advertising or signage purposes, or for a television orcomputer monitor screen, and, in short, for any purpose desiringsomething to be displayed.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hand-held instrument projecting animage at a working distance therefrom;

FIG. 2 is an enlarged, overhead, perspective view of an image projectionarrangement in accordance with this invention for installation in theinstrument of FIG. 1;

FIG. 3 is a top plan view of the arrangement of FIG. 2;

FIG. 4 is a perspective front view of an inertial drive for use in thearrangement of FIG. 2;

FIG. 5 is a perspective rear view of the inertial drive of FIG. 4;

FIG. 6 is a perspective view of a practical implementation of thearrangement of FIG. 2;

FIG. 7 is an electrical schematic block diagram depicting operation ofthe arrangement of FIG. 2;

FIG. 8 is a perspective schematic view of part of an image projectionarrangement for projecting an image with undesirable curved scan linesin accordance with the prior art;

FIG. 9 is a perspective schematic view of part of an image projectionarrangement for projecting an image with linear scan lines in accordancewith this invention;

FIG. 10 is an enlarged front elevational view of a raster pattern withlinear scan lines projected by the arrangement of FIG. 9;

FIG. 11 is a perspective, enlarged view of part of the image projectionarrangement of FIG. 2, depicting part of the optical path of the laserbeam; and

FIG. 12 is an enlarged, side elevational view of FIG. 11, againdepicting the optical path of the laser beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference numeral 10 in FIG. 1 generally identifies a hand-heldinstrument, for example, a personal digital assistant, in which alightweight, compact, image projection arrangement 20, as shown in FIG.2, is mounted and operative for projecting a two-dimensional color imageon a generally planar projection surface at a variable distance from theinstrument. By way of example, an image 18 is situated within a workingrange of distances relative to the instrument 10.

As shown in FIG. 1, the image 18 extends over an optical horizontal scanangle A extending along the horizontal direction, and over an opticalvertical scan angle B extending along the vertical direction, of theimage. As described below, the image is comprised of illuminated andnon-illuminated pixels on a raster pattern of scan lines swept by ascanner in the arrangement 20.

The parallelepiped shape of the instrument 10 represents just one formfactor of a housing in which the arrangement 20 may be implemented. Theinstrument can be shaped with many different form factors, such as apen, a cellular telephone, a clamshell or a wristwatch.

In the preferred embodiment, the arrangement 20 measures less than about30 cubic centimeters in volume. This compact, miniature size allows thearrangement 20 to be mounted in housings of many diverse shapes, largeor small, portable or stationary, including some having an on-boarddisplay 12, a keypad 14, and a window 16 through which the image isprojected.

Referring to FIGS. 2 and 3, the arrangement 20 includes a solid-state,preferably a semiconductor laser 22 which, when energized, emits abright red laser beam at about 635-655 nanometers. Lens 24 is abiaspheric convex lens having a positive focal length and is operativefor collecting virtually all the energy in the red beam and forproducing a diffraction-limited beam. Lens 26 is a concave lens having anegative focal length. Lenses 24, 26 are held by non-illustratedrespective lens holders apart on a support (not illustrated in FIG. 2for clarity) inside the instrument 10. The lenses 24, 26 shape the redbeam profile over the working distance.

Another solid-state, semiconductor laser 28 is mounted on the supportand, when energized, emits a diffraction-limited blue laser beam atabout 430-480 nanometers. Another biaspheric convex lens 30 and aconcave lens 32 are employed to shape the blue beam profile in a manneranalogous to lenses 24, 26.

A green laser beam having a wavelength on the order of 530 nanometers isgenerated not by a semiconductor laser, but instead by a green module 34having an infrared diode-pumped YAG crystal laser whose output beam at1060 nanometers. A non-linear frequency doubling crystal is included inthe infrared laser cavity between two laser mirrors. Since the infraredlaser power inside the cavity is much larger than the power coupledoutside the cavity, the frequency doubler is more efficient ingenerating the double frequency green light inside the cavity. Theoutput mirror of the laser is reflective to the 1060 nm infraredradiation, and transmissive to the doubled 530 nm green laser beam.Since the correct operation of the solid-state laser and frequencydoubler require precise temperature control, a semiconductor devicerelying on the Peltier effect is used to control the temperature of thegreen laser module. The thermo-electric cooler can either heat or coolthe device depending on the polarity of the applied current. Athermistor is part of the green laser module in order to monitor itstemperature. The readout from the thermistor is fed to a controller,which adjusts the control current to the thermoelectric cooleraccordingly.

As explained below, the lasers are pulsed in operation at frequencies onthe order of 100 MHz. The red and blue semiconductor lasers 22, 28 canbe pulsed at such high frequencies, but the currently available greensolid-state lasers cannot. As a result, the green laser beam exiting thegreen module 34 is pulsed with an acousto-optical modulator 36 whichcreates an acoustic traveling wave inside a crystal for diffracting thegreen beam. The modulator 36, however, produces a zero-order,non-diffracted beam 38 and a first-order, pulsed, diffracted beam 40.The beams 38, 40 diverge from each other and, in order to separate themto eliminate the undesirable zero-order beam 38, the beams 38, 40 arerouted along a long, folded path having a folding mirror 42.Alternatively, an electro-optical modulator can be used eitherexternally or internally to the green laser module to pulse the greenlaser beam. Other possible ways to modulate the green laser beam includeelectro-absorption modulation, or Mach-Zender interferometer. The beams38, 40 are routed through positive and negative lenses 44, 46. However,only the diffracted green beam 40 is allowed to impinge upon, andreflect from, the folding mirror 48. The non-diffracted beam 38 isabsorbed by an absorber 50, preferably mounted on the mirror 48.

The arrangement includes a pair of dichroic filters 52, 54 arranged tomake the green, blue and red beams as collinear as possible beforereaching a scanning assembly 60. Filter 52 allows the green beam 40 topass therethrough, but the blue beam 56 from the blue laser 28 isreflected by the interference effect. Filter 54 allows the green andblue beams 40, 56 to pass therethrough, but the red beam 58 from the redlaser 22 is reflected by the interference effect.

The nearly collinear beams 40, 56, 58 are directed to, and reflectedoff, a stationary fold mirror 62. The scanning assembly 60 includes afirst scan mirror 64 oscillatable by an inertial drive 66 (shown inisolation in FIGS. 4-5) at a first scan rate to sweep the laser beamsreflected off the fold mirror 62 over the first horizontal scan angle A,and a second scan mirror 68 oscillatable by an electromagnetic drive 70at a second scan rate to sweep the laser beams reflected off the firstscan mirror 64 over the second vertical scan angle B. In a variantconstruction, the scan mirrors 64, 68 can be replaced by a singletwo-axis mirror.

The inertial drive 66 is a high-speed, low electrical power-consumingcomponent. Details of the inertial drive can be found in U.S. patentapplication Ser. No. 10/387,878, filed Mar. 13, 2003, assigned to thesame assignee as the instant application, and incorporated herein byreference thereto. The use of the inertial drive reduces powerconsumption of the scanning assembly 60 to less than one watt and, inthe case of projecting a color image, as described below, to less thanten watts.

The drive 66 includes a movable frame 74 for supporting the scan mirror64 by means of a hinge that includes a pair of collinear hinge portions76, 78 extending along a hinge axis and connected between oppositeregions of the scan mirror 64 and opposite regions of the frame. Theframe 74 need not surround the scan mirror 64, as shown.

The frame, hinge portions and scan mirror are fabricated of a one-piece,generally planar, silicon substrate, which is approximately 150μ thick.The silicon is etched to form omega-shaped slots having upper parallelslot sections, lower parallel slot sections, and U-shaped central slotsections. The scan mirror 64 preferably has an oval shape and is free tomove in the slot sections. In the preferred embodiment, the dimensionsalong the axes of the oval-shaped scan mirror measure 749μ×1600μ. Eachhinge portion measures 27μ in width and 1130μ in length. The frame has arectangular shape measuring 3100μ in width and 4600μ in length.

The inertial drive is mounted on a generally planar, printed circuitboard 80 and is operative for directly moving the frame and, by inertia,for indirectly oscillating the scan mirror 64 about the hinge axis. Oneembodiment of the inertial drive includes a pair of piezoelectrictransducers 82, 84 extending perpendicularly of the board 80 and intocontact with spaced apart portions of the frame 74 at either side ofhinge portion 76. An adhesive may be used to insure a permanent contactbetween one end of each transducer and each frame portion. The oppositeend of each transducer projects out of the rear of the board 80 and iselectrically connected by wires 86, 88 to a periodic alternating voltagesource (not shown).

In use, the periodic signal applies a periodic drive voltage to eachtransducer and causes the respective transducer to alternatingly extendand contract in length. When transducer 82 extends, transducer 84contracts, and vice versa, thereby simultaneously pushing and pullingthe spaced apart frame portions and causing the frame to twist about thehinge axis. The drive voltage has a frequency corresponding to theresonant frequency of the scan mirror. The scan mirror is moved from itsinitial rest position until it also oscillates about the hinge axis atthe resonant frequency. In a preferred embodiment, the frame and thescan mirror are about 150μ thick, and the scan mirror has a high Qfactor. A movement on the order of 1μ by each transducer can causeoscillation of the scan mirror at scan angles in excess of 15°.

Another pair of piezoelectric transducers 90, 92 extends perpendicularlyof the board 80 and into permanent contact with spaced apart portions ofthe frame 74 at either side of hinge portion 78. Transducers 90, 92serve as feedback devices to monitor the oscillating movement of theframe and to generate and conduct electrical feedback signals alongwires 94, 96 to a feedback control circuit (not shown).

Although light can reflect off an outer surface of the scan mirror, itis desirable to coat the surface of the mirror 64 with a specularcoating made of gold, silver, aluminum, or a specially designed highlyreflective dielectric coating.

The electromagnetic drive 70 includes a permanent magnet jointly mountedon and behind the second scan mirror 68, and an electromagnetic coil 72operative for generating a periodic magnetic field in response toreceiving a periodic drive signal. The coil 72 is adjacent the magnet sothat the periodic field magnetically interacts with the permanent fieldof the magnet and causes the magnet and, in turn, the second scan mirror68 to oscillate.

The inertial drive 66 oscillates the scan mirror 64 at a high speed at ascan rate preferably greater than 5 kHz and, more particularly, on theorder of 18 kHz or more. This high scan rate is at an inaudiblefrequency, thereby minimizing noise and vibration. The electromagneticdrive 70 oscillates the scan mirror 68 at a slower scan rate on theorder of 40 Hz which is fast enough to allow the image to persist on ahuman eye retina without excessive flicker.

The faster mirror 64 sweeps a generally horizontal scan line, and theslower mirror 68 sweeps the generally horizontal scan line vertically,thereby creating a raster pattern which is a grid or sequence of roughlyparallel scan lines from which the image is constructed. Each scan linehas a number of pixels. The image resolution is preferably XGA qualityof 1024×768 pixels. Over a limited working range, a high-definitiontelevision standard, denoted 720p, 1270×720 pixels, can be obtained. Insome applications, a one-half VGA quality of 320×480 pixels, orone-fourth VGA quality of 320×240 pixels, is sufficient. At minimum, aresolution of 160×160 pixels is desired.

The roles of the mirrors 64, 68 could be reversed so that mirror 68 isthe faster, and mirror 64 is the slower. Mirror 64 can also be designedto sweep the vertical scan line, in which event, mirror 68 would sweepthe horizontal scan line. Also, the inertial drive can be used to drivethe mirror 68. Indeed, either mirror can be driven by anelectromechanical, electrical, mechanical, electrostatic, magnetic, orelectromagnetic drive.

The slow-mirror is operated in a constant velocity sweep-mode duringwhich time the image is displayed. During the mirror's return, themirror is swept back into the initial position at its natural frequency,which is significantly higher. During the mirror's return trip, thelasers can be powered down in order to reduce the power consumption ofthe device.

FIG. 6 is a practical implementation of the arrangement 20 in the sameperspective as that of FIG. 2. The aforementioned components are mountedon a support, which includes a top cover 100 and a support plate 102.Holders 104, 106, 108, 110, 112 respectively hold folding mirrors 42,48, filters 52, 54 and fold mirror 62 in mutual alignment. Each holderhas a plurality of positioning slots for receiving positioning postsstationarily mounted on the support. Thus, the mirrors and filters arecorrectly positioned. As shown, there are three posts, therebypermitting two angular adjustments and one lateral adjustment. Eachholder can be glued in its final position.

The image is constructed by selective illumination of the pixels in oneor more of the scan lines. As described below in greater detail withreference to FIG. 7, a controller 114 causes selected pixels in theraster pattern to be illuminated, and rendered visible, by the threelaser beams. For example, red, blue and green power controllers 116,118, 120 respectively conduct electrical currents to the red, blue andgreen lasers 22, 28, 34 to energize the latter to emit respective lightbeams at each selected pixel, and do not conduct electrical currents tothe red, blue and green lasers to deenergize the latter tonon-illuminate the other non-selected pixels. The resulting pattern ofilluminated and non-illuminated pixels comprises the image, which can beany display of human- or machine-readable information or graphic.

Referring to FIG. 1, the raster pattern is shown in an enlarged view.Starting at an end point, the laser beams are swept by the inertialdrive along the generally horizontal direction at the horizontal scanrate to an opposite end point to form a scan line. Thereupon, the laserbeams are swept by the electromagnetic drive 70 along the verticaldirection at the vertical scan rate to another end point to form asecond scan line. The formation of successive scan lines proceeds in thesame manner.

The image is created in the raster pattern by energizing or pulsing thelasers on and off at selected times under control of the microprocessor114 or control circuit by operation of the power controllers 116, 118,120. The lasers produce visible light and are turned on only when apixel in the desired image is desired to be seen. The color of eachpixel is determined by one or more of the colors of the beams. Any colorin the visible light spectrum can be formed by the selectivesuperimposition of one or more of the red, blue, and green lasers. Theraster pattern is a grid made of multiple pixels on each line, and ofmultiple lines. The image is a bit-map of selected pixels. Every letteror number, any graphical design or logo, and even machine-readable barcode symbols, can be formed as a bit-mapped image.

As shown in FIG. 7, an incoming video signal having vertical andhorizontal synchronization data, as well as pixel and clock data, issent to red, blue and green buffers 122, 124, 126 under control of themicroprocessor 114. The storage of one full VGA frame requires manykilobytes, and it would be desirable to have enough memory in thebuffers for two full frames to enable one frame to be written, whileanother frame is being processed and projected. The buffered data issent to a formatter 128 under control of a speed profiler 130 and tored, blue and green look up tables (LUTs) 132, 134, 136 to correctinherent internal distortions caused by scanning, as well as geometricaldistortions caused by the angle of the display of the projected image.The resulting red, blue and green digital signals are converted to red,blue and green analog signals by digital to analog converters (DACs)138, 140, 142. The red and blue analog signals are fed to red and bluelaser drivers (LDs) 144, 146 which are also connected to the red andblue power controllers 116, 118. The green analog signal is fed to anacousto-optical module (AOM) radio frequency (RF) driver 150 and, inturn, to the green laser 34 which is also connected to a green LD 148and to the green power controller 120.

Feedback controls are also shown in FIG. 7, including red, blue andgreen photodiode amplifiers 152, 154, 156 connected to red, blue andgreen analog-to-digital (A/D) converters 158, 160, 162 and, in turn, tothe microprocessor 114. Heat is monitored by a thermistor amplifier 164connected to an A/D converter 166 and, in turn, to the microprocessor.

The scan mirrors 64, 68 are driven by drivers 168, 170 which are fedanalog drive signals from DACs 172, 174 which are, in turn, connected tothe microprocessor. Feedback amplifiers 176, 178 detect the position ofthe scan mirrors 64, 68, and are connected to feedback A/Ds 180, 182and, in turn, to the microprocessor.

A power management circuit 184 is operative to minimize power whileallowing fast on-times, preferably by keeping the green laser on all thetime, and by keeping the current of the red and blue lasers just belowthe lasing threshold.

A laser safety shut down circuit 186 is operative to shut the lasers offif either of the scan mirrors 64, 68 is detected as being out ofposition.

Turning now to FIG. 8, a scan mirror 200 is depicted as beingoscillatable about a scan axis 202. A generally planar projectionsurface 204 is depicted at a distance from the scan mirror. Also shownis a plane 206 perpendicular to the scan axis 202. In the prior art, anincoming laser beam is situated above or below the plane 206 and, as aresult, the laser beam is swept as a curved scan line 208 on theprojection surface 204. An image comprised of a plurality of such curvedscan lines spaced generally apart along the scan axis 202 will bedistorted and it is difficult to electronically correct for suchdistortion.

FIG. 9 is analogous to FIG. 8, and like parts are identified with likereference numerals. In the invention of FIG. 9, the incoming laser beamis directed along an optical path in the plane 206 that is perpendicularto the scan axis 202. As a result, the laser beam is swept as a linearscan line 210 on the projection surface 204. An image comprised of aplurality of such linear scan lines spaced generally apart along thescan axis 202 will not be distorted. FIG. 10 depicts a plurality of thelinear scan lines 210, each scan line being tilted as a result ofscanning by another scan mirror, but not curved.

FIGS. 11-12 depict the path of the incoming composite laser beam amongthe fold mirror 62, the fast scan mirror 64 of the drive 66, and theslow scan mirror 68 of the drive 70. The composite laser beam 40, 56, 58is directed to the inclined fold mirror 62, which is preferably mountedon the support at an angle of inclination of 15° from the vertical, forreflection therefrom as a sub-beam 212 (see FIG. 11) to the fast scanmirror 64. As best seen in FIG. 12, the fast scan mirror 64 oscillatesabout a scan axis 214, and is preferably mounted on the support at anangle of inclination of 30° from the horizontal. The sub-beam 212 isdirected in a plane perpendicular to the scan axis 214 for reflectionfrom the fast scan mirror 64 as a sub-beam 216 to the slow scan mirror68. The projection of the sub-beam 216 on the slow scan mirror 68 is astraight, uncurved line. The sub-beam 216 is reflected from the slowscan mirror 68 as a raster pattern of linear scan lines (see FIG. 10).The slow scan mirror 68 is oscillatable about a scan axis that isgenerally parallel to the scan axis 214, and is preferably mounted onthe support at an angle of inclination of 33.75° from the horizontal asseen in the side view of FIG. 12.

If a single two-axis mirror is employed to replace the pair of fast andslow scan mirrors, curved scan lines will result, even if the incominglaser beam lies in the plane perpendicular to one of the scan axes,because, at any moment, the one scan axis is always rotating in theorthogonal direction (along the slow scan direction). Hence, in thatevent, the invention proposes rotating the fold mirror synchronouslywith the slow scan mirror.

It will be understood that each of the elements described above, or twoor more together, also may find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in anarrangement for and a method of projecting an image with linear scanlines, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. An image projection arrangement for projecting a two-dimensionalimage on a generally planar projection surface, the arrangementincluding: a laser assembly for directing a laser beam along an opticalpath; a scanner including a scan mirror oscillatable about a scan axis,for sweeping the laser beam as a pattern of scan lines duringoscillation of the scan mirror at a distance from the laser assembly onthe projection surface, each scan line having a number of pixels; and acontroller operatively connected to the laser assembly and the scanner,for causing selected pixels along the scan lines to be illuminated, andrendered visible, by the laser beam to produce the image; wherein thelaser assembly includes a plurality of lasers for respectivelygenerating a plurality of laser beams of different wavelengths, and anoptical assembly for focusing and nearly collinearly arranging the laserbeams to form the laser beam as a composite beam which is directed tothe scan mirror, and wherein the lasers include red and bluesemiconductor lasers for respectively generating red and blue laserbeams, and wherein the lasers include a diode-pumped YAG laser andoptical frequency doubler for producing a green laser beam; wherein thearrangement is characterized by: the laser assembly directs the laserbeam to travel in a plane perpendicular to the scan axis to cause eachscan line to be linear, and the illuminated pixels are visible only onlinear scan lines to reduce distortion of the image.
 2. The imageprojection arrangement of claim 1, wherein the scan mirror is operativefor sweeping the composite beam along a first linear direction at afirst scan rate and over a first scan angle, and wherein the scannerincludes another oscillatable scan mirror for sweeping the compositebeam along a second direction substantially perpendicular to the firstlinear direction, and at a second scan rate different from the firstscan rate, and at a second scan angle different from the first scanangle.
 3. The image projection arrangement of claim 2, wherein at leastone of the scan mirrors is oscillated by an inertial drive.
 4. The imageprojection arrangement of claim 2, and a support for supporting thelaser assembly and the scanner, and wherein the optical assemblyincludes a fold mirror mounted on the support at an angle of inclinationfor directing the composite laser beam along the plane perpendicular tothe scan axis.
 5. The image projection arrangement of claim 1, whereinthe controller includes means for energizing the laser assembly toilluminate the selected pixels, and for deenergizing the laser assemblyto non-illuminate pixels other than the selected pixels.
 6. The imageprojection of claim 1, wherein the controller includes means foreffectively aligning the laser beams collinearly by delaying turning onand off the pixels of each of the laser beams relative to each other.